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Improving the repeatability of Heidelberg retina tomograph and Heidelberg retina tomograph II rim area measurements
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  1. N G Strouthidis1,2,
  2. E T White1,
  3. V M F Owen3,
  4. T A Ho1,
  5. D F Garway-Heath1,2
  1. 1Glaucoma Research Unit, Moorfields Eye Hospital, London, UK
  2. 2Institute of Ophthalmology, London, UK
  3. 3School of Biomedical and Natural Sciences, Nottingham Trent University, Nottingham, UK
  1. Correspondence to: D F Garway-Heath MD, FRCOphth, Glaucoma Research Unit, Moorfields Eye Hospital, 162 City Road, London EC1V 2PD, UK; david.garway-heathmoorfields.nhs.uk

Abstract

Aims: To devise and test strategies for improving Heidelberg retina tomograph (HRT and HRT-II) rim area (RA) repeatability and assess the benefit of the strategies in time series of HRT images.

Methods: The effect of the standard and 320 μm reference planes and image quality on RA repeatability was assessed in a test-retest HRT image dataset from 74 subjects. A longitudinal HRT image dataset from 30 ocular hypertensive subjects was analysed by linear regression of RA over time, with each of the reference planes and using a manual image alignment facility. RA variability was estimated by comparing the standard deviation of residuals (RSD) generated by each linear regression.

Results: RA repeatability was better with the 320 μm reference plane (repeatability coefficient 0.17 mm2), improving further with only good quality images (repeatability coefficient 0.08 mm2). For the longitudinal data, a significant (p<0.0001) reduction in the RSD from 0.10 to 0.05 mm2 was obtained with the 320 μm reference plane. Manual alignment led to a further significant (p<0.0001) reduction in the RSD to 0.04 mm2.

Conclusions: The findings support the use of a 320 μm reference plane and manual image alignment to analyse RA over time. The estimates of RA repeatability may be used to define thresholds for glaucomatous change.

  • HRT, Heidelberg retina tomograph
  • OHT, ocular hypertension
  • ONH, optic nerve head
  • POAG, primary open angle glaucoma
  • RA, rim area
  • RSD, residual standard deviation
  • VF, visual field
  • Heidelberg retina tomograph
  • glaucoma
  • HRT, Heidelberg retina tomograph
  • OHT, ocular hypertension
  • ONH, optic nerve head
  • POAG, primary open angle glaucoma
  • RA, rim area
  • RSD, residual standard deviation
  • VF, visual field
  • Heidelberg retina tomograph
  • glaucoma

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Footnotes

  • Competing interests: NGS was funded by a Friends of Moorfields research fellowship and through an unrestricted grant from Heidelberg Engineering.